Scientists from NUST MISIS developed a unique composite material that can be used in harsh temperature conditions, such as those in nuclear reactors. The microhardness of the sandwich material is 3 times higher compared to the microhardness of its individual components. These properties withstand temperatures up to 700°C (1,300°F). The results of the research were published in Materials Letters.
To create a new generation of fast-neutron reactors, new structural materials are needed, because the steel, which is considered for use in the shells of fuel elements, is unable to withstand the required heating of 550-700°C (1,000-1,300°F) .
One of the ways to obtain harder materials is the creation of composites by methods of severe plastic deformation (SPD), that is, deformation in special machines under high pressure. As a result, composite materials that are harder than their individual components are obtained. At the same time, a smaller, nanocrystalline structure is formed in the material, demonstrating rapid grain growth when heated. Hence, such materials have low thermal stability and lose microhardness when heated.
![NUST MISIS Laboratory for Hybrid Nanostructured Materials](https://scitechdaily.com/images/NUST-MISIS-Laboratory-for-Hybrid-Nanostructured-Materials-777x518.jpg)
This is the team of the NUST MISIS Laboratory for Hybrid Nanostructured Materials. © Sergey Gnuskov/NUST MISIS
Scientists from NUST MISIS Laboratory for Hybrid Nanostructured Materials found a way to increase both the microhardness and the thermal stability of the composite material. For this, scientists used one of SPD methods, i.e. high-pressure torsion (HPT), which allowed the creation of a specific multilayer structure with vanadium alloy.
“We created a sample with 0,5 mm and 0,3 mm steel layers, adding 0,2 mm vanadium alloy in between. Hence, the overall thickness of the sample was 1 mm. During the HPT, the sample is placed between two flat-base strikers and compressed under an applied pressure of several HPa. The lower striker rotates and the surface friction forces the sample to deform by shear. As a result, we obtained a thin multilayer structure.” — Stanislav Rogachev, Head of the Research
Evaluation of the resulting sample showed that after HPT, the strength of the “sandwich” increased by 3 times compared to the strength of each of the individual components. Moreover, the multilayer structure enabled the final material to withstand heat up to 700°C (1,300°F). Thus, for the first time, a composite nanostructured sandwich material with such high thermal stability was obtained. Such material is promising for use in a number of high-tech areas, for example, in the previously mentioned nuclear reactors.
Next, scientists plan to continue experiments on SPD of metal composites. Specifically, the team is going to work with steel/zirconium, steel/copper, and steel/aluminum combinations.
Reference: “High thermally stable multi-layer steel/vanadium alloy hybrid material obtained by high-pressure torsion” by S. O. Rogachev, V. M. Khatkevich, S. A. Nikulin, M. V. Ignateva and A. A. Gromov, 9 August 2019, Materials Letters.
DOI: 10.1016/j.matlet.2019.126527
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